Evolutionary relationships among the Protostromgylidae (Nematoda : Metastrongyloidea) as inferred from morphological characters, with consideration of parasite-host coevolution

The phylogeny of nematodes in the family Protostrongylidae (Nematoda: Metas trongyloidea) was reconstructed by cladistic analysis of 28 binary and mult istate characters derived from comparative morphology. Analyses were hierar chical, and examined (1) relationships among genera, including 13 ingroup t axa and Metastrongylidae as an outgroup (single tree, 78 steps, consistency index [CT] = 0.705); and (2) relationships among genera and species groups , including 21 ingroup taxa and Metastrongylus apri as an outgroup (single tree, 76 steps, CI = 0.582). In the species-level tree, Protostrongylidae w as divided into 2 major clades, 1 containing the subfamilies Muelleriinae i ncluding the recently described (Umingmakstrongylus pallikuukensis). Elapho strongylinae, and the Varestrongylinae (excluding Pneumrocaulus kadenazii). Varestrongylus was paraphyletic as it included Pneumostrongylus calcaratus . The second major clade consisted of a paraphyletic group containing Proto strongylus spp. and Spiculcaulus leuckarti,ti and, basal to this subclade, several other individual protostrongylid lineages. The various subclades ge nerally correspond to the subfamilial divisions of the Protostrongylidae. T he Neostrongylinae, however, is not supported as Neostrongylus and Orthostr ongylus are not sister groups. Based on a large number of hypothesized syna pomorphies, the elaphostrongylines appear to be a highly derived group of p rotostrongylids, a feature potentially correlated with their habitat locali zation in muscular and nervous tissues. The generic-level tree retained mos t of the primary structure revealed among the species but excluded the vare strongylines from the Muelleriinae; Elaphostrongylinae subclade. Artiodacty les of the family Cervidae are considered basal hosts for protostrongylids; secondary colonization in Caprini, Rupicaprini, and among lagomorphs is po stulated.